Field of the Invention
The present invention relates to an air secondary battery and more specifically to an air secondary battery containing a positive electrode having a matrix and an oxygen-containing gas passage formed in the matrix.
Description of the Related Art
Air batteries are electric batteries using oxygen as a positive electrode active material. Air primary batteries using zinc as a negative electrode active material have been widely used, and air secondary batteries, which are rechargeable, have been studied in recent years. In terms of high energy density, using of lithium as a negative electrode active material has been attempted in the air secondary batteries. However, as described in Peter G. Bruce, et al., NATURE MATERIALS, vol. 11, no. 1, pp. 19-29 (2012), the conventional air secondary batteries are disadvantageous in that the electric capacitance (or the cycle characteristic) tends to be deteriorated as a result of repeating the charge and discharge cycles and that the overpotential is large in the charge process.
As described in U.S. Pat. No. 8,632,920 and U.S. Patent Application Publication No. 2011/0200891, the above disadvantages are caused because air bubbles stay and accumulate on the boundary between the positive electrode and the electrolyte while the charge and discharge cycles are repeated, whereby the positive electrode is covered with the air bubbles. To solve this problem, U.S. Pat. No. 8,632,920 proposes that a permeation preventing layer for preventing oxygen permeation is formed on a surface of the positive electrode that faces the negative electrode.
U.S. Patent Application Publication No. 2011/0200891 proposes a conductive porous body disposed in the positive electrode. The air bubbles accumulated on the boundary between the positive electrode and the electrolyte are diffused and removed from the boundary to an oxygen supply port through the conductive porous body.
Furthermore, Japanese Laid-Open Patent Publication No. 2010-257839 discloses an air secondary battery having a positive electrode wherein the positive electrode is formed as a stack of first and second layers each having a catalyst, and the pore diameter of the first layer is different from that of the second layer. Therefore, even when the positive electrode has a large thickness, an oxygen-containing gas can be sufficiently diffused in the positive electrode.